This invention relates to the use of zeolite powders in sheets and films of thermoplastic resins as antiblock materials. In particular, zeolites of specific compositions are effective antiblocks and provide unexpected physical properties of the finished sheet or film.
Thermoplastic resins, such as polyolefins and the like, often find use as sheets and films. Such sheets are stacked and films are rolled in storage and use. The sheets and/or films are adherent and may be difficult or nearly impossible to separate for use. Various inorganic materials, such as silica or diatomaceous earth, can be incorporated into the resin prior to forming the sheet or film to prevent such adherence. These materials are called antiblocks, the adherence being called blocking.
U.S. Pat. No. 4,250,081 teaches that zeolite powders of various types can be used as antiblocks. This patent distinguishes zeolites over the prior art siliceous antiblock by indicating the zeolites to be hydrated, while the prior art materials must be nearly water-free, and zeolites can be blended with the thermoplastic more easily. The patent indicates that Zeolite A containing 24% water (fully hydrated) can be processed at over 170.degree. C. to provide antiblock properties.